Methods and apparatus employed to cast pre-tensioned concrete structural panels, are generally labour intensive and are not adapted to easily cast the panels with an aperture for a window, a door or other purpose. Still further, the formwork employed is only designed to manufacture a single sized panel. Still further, the decorative treatments of the panel faces are limited by the current methods of manufacture. Still further, the methods of prevention of water ingress from the external face to the internal panel face are inadequate or subject to poor on-site work practices. Still further, the methods of sealing openings in panels for doors or windows are limited by the life of the sealants used.
In the prior art, a batch-type process has been employed to more efficiently manufacture cast pre-tensioned concrete structural members in the form of panels, to be used, for example, as walls, floors or roofs in building construction. In a batch-type process, a long concrete slab or plank is poured and cured, and thereafter cut into a plurality of shorter length panels. Due to the relatively long curing time required, this batch-type process is more efficient than casting individual shorter panels because a large number of individual panels can be produced at substantially the same time. The length of the slab, before cutting into shorter individual panels, may be as much as 150 meters with the slab weighing 230,000 kg.
Generally, there are two batch-type methods employed for use in the manufacture of pre-tensioned concrete structural panels, either a fixed bed apparatus of the general type described in U.S. Pat. No. 3,217,375 of Kinnard, or a moving bed apparatus of the type described in U.S. Pat. No. 3,523,343 of Mitchell.
In the U.S. Pat. No. 3,217,375 of Kinnard, the pre-tensioned concrete structural member, including core openings therein, is produced on a long stationary casting bed by means of a hopper and roller units and a casting machine which travels the length of the bed. The completed member is then cured and subsequently cut into the desired lengths.
The U.S. Pat. No. 3,523,343 of Mitchell, describes a moving bed system wherein a manufacturing area contains sequentially used items of production equipment, suitably housed and located centrally between an elongated curing area and a similarly elongated unloading overrun area. A casting bed moves back and forth several times during each production cycle while the various operations of the manufacturing process are performed. The casting bed comprises a lengthy stress frame which is mounted on a track extending the full length of the facility and carries a moulding form in which the pre-tensioned concrete member is cast by equipment which remains stationary in the manufacturing area while the bed moves beneath it.
In the above described processes, the concrete slab is pre-tensioned by means of reinforcing strands or tendons longitudinally tensioned between the ends of the casting bed prior to the casting of concrete. After the concrete is cured, the ends of the tendons are released to transfer the stress to the concrete and then the slab is cut into a plurality of shorter individual panels. The pre-tensioned panels produced offer superior performance to panels made using conventional reinforcement, however, there are several limitations with these methods of manufacture, including the large size of the casting beds, apertures for window or door openings are not easily made, the cutting of the slab into a plurality of shorter individual panels produces large quantities of concrete sludge, the diamond cutting wheels employed to cut the concrete are expensive and wear rapidly, the individual panels produced by cutting the slab are not adapted for easy lifting from the casting bed, and connection of the individual panels to other building elements is not readily achieved.